1. Field of the Invention
The present invention relates to an electrostatic recording apparatus for which a belt-roller transfer system is adapted to transfer a toner image from a toner image retainer onto a transfer material.
2. Description of the Prior Art
In a recording (reproducing) process of an electrophotographic system, corona discharge of a direct current or an alternating current has usually been used for transfer/separation in almost all cases. This is probably because a relatively stable performance is obtained by a simple structure under the limited conditions of the quantity of sticking toner, a change in environment and a transfer material (paper for transfer).
However, the application of the usual transfer system has limitations in a process wherein about three times as much quantity of toner as usual needs to be transferred as in the case of toner, such as magnetic toner, which has high dependence on the environment in transfer, or in the case of color copying.
Accordingly, a belt transfer system has been studied and examined heretofore, and this system has been regarded as enabling the attainment of a high performance theoretically.
There are few examples of its practical application, however, due to technical problems and the problem of the cost accompanying this system. A system using a belt of high resistance and a corona discharge electrode can be cited as the example of said system having been put to practical use. However, a strict control on the occurrence of ozone has been requested recently and therefore a system not using corona discharge is desired.
In order to meet this demand, the present inventor has developed a transfer separation unit of a belt-roller transfer system, wherein an endless-form transfer material conveyance belt is pressed toward a photosensitive member by an electrode roller and a transfer material is made to proceed between this transfer material conveyance belt and the electrode roller so that a toner image on the photosensitive member be transferred onto the transfer material.
In this belt-roller transfer system, however, it has been difficult to detach reliably from the photosensitive member the transfer material whereon the toner image is transferred.